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@Article { 4796,
title = {Object features used by humans and monkeys to identify rotated shapes},
journal = {Journal of Vision},
year = {2008},
month = {2},
volume = {8},
number = {2:9},
pages = {1-15},
abstract = {Humans and rhesus monkeys can identify shapes that have been rotated in the picture plane. Recognition of rotated shapes can be as efficient as recognition of upright shapes. Here we investigate whether subjects showing view-invariant performance use the same object features to identify upright and rotated versions of a shape. We find marked differences between humans and monkeys. While humans tend to use the same features independent of shape orientation, monkeys use unique features for each orientation. Humans are able to generalize to a greater degree across orientation changes than rhesus monkey observers, who tend to relearn separate problems at each orientation rather than flexibly apply previously learned knowledge to novel problems.},
department = {Department Logothetis},
web_url = {http://journalofvision.org/8/2/9/Nielsen-2008-jov-8-2-9.pdf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
DOI = {10.1167/8.2.9},
author = {Nielsen, KJ and Logothetis, NK and Rainer, G}
}
@Article { 4316,
title = {Object Recognition: Similar Visual Strategies of Birds and Mammals},
journal = {Current Biology},
year = {2007},
month = {3},
volume = {17},
number = {5},
pages = {R174-R176},
abstract = {Behavioral testing has revealed that pigeons may use the same visual information sources as humans to discriminate between three-dimensional shapes.},
department = {Department Logothetis},
web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6VRT-4N689JT-K-3\&_cdi=6243\&_user=29041\&_orig=browse\&_coverDate=03\%2F06\%2F2007\&_sk=999829994\&view=c\&wchp=dGLbVtz-zSkWb\&md5=1af621df50c1268dd8c291426ace0718\&ie=/sdarticle.pdf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
DOI = {10.1016/j.cub.2007.01.014},
author = {Nielsen, KJ and Rainer, G}
}
@Article { 4140,
title = {Dissociation Between Local Field Potentials and Spiking Activity in Macaque Inferior Temporal Cortex Reveals Diagnosticity-Based Encoding of Complex Objects},
journal = {Journal of Neuroscience},
year = {2006},
month = {9},
volume = {26},
number = {38},
pages = {9639-9645},
abstract = {Neurons in the inferior temporal (IT) cortex respond selectively to complex objects, and maintain their selectivity despite partial occlusion. However, relatively little is known about how the occlusion of different shape parts influences responses in the IT cortex. Here, we determine experimentally which parts of complex objects monkeys are relying on in a discrimination task. We then study the effect of occlusion of parts with different behavioral relevance on neural responses in the IT cortex at the level of spiking activity and local field potentials (LFPs). For both spiking activity and LFPs, we found that the diagnostic object parts, which were important for behavioral judgments, were preferentially represented in the IT cortex. Our data show that the effects of diagnosticity grew systematically stronger along a posterioranterior axis for LFPs, but were evenly distributed for single units, suggesting that diagnosticity is first encoded in the posterior IT cortex. Our findings highlight the power of co
mbined analysis of field potentials and spiking activity for mapping structure to computational function in the brain.},
department = {Department Logothetis},
web_url = {http://www.jneurosci.org/cgi/reprint/26/38/9639},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
DOI = {10.1523/JNEUROSCI.2273-06.2006},
author = {Nielsen, K and Logothetis, NK and Rainer, G}
}
@Article { 3820,
title = {Discrimination Strategies of Humans and Rhesus Monkeys for Complex Visual Displays},
journal = {Current Biology},
year = {2006},
month = {4},
volume = {16},
number = {8},
pages = {814-820},
abstract = {By learning to discriminate among visual stimuli, human observers can become experts at specific visual tasks. The same is true for Rhesus monkeys, the major animal model of human visual perception. Here, we systematically compare how humans and monkeys solve a simple visual task. We trained humans and monkeys to discriminate between the members of small natural-image sets. We employed the Bubbles procedure [1] to determine the stimulus features used by the observers. On average, monkeys used image features drawn from a diagnostic region covering about 7\% ± 2\% of the images. Humans were able to use image features drawn from a much larger diagnostic region covering on average 51\% ± 4\% of the images. Similarly for the two species, however, about 2\% of the image needed to be visible within the diagnostic region on any individual trial for correct performance. We characterize the low-level image properties of the diagnostic regions and discuss individual differences among the monkeys. Our results reveal tha
t monkeys base their behavior on confined image patches and essentially ignore a large fraction of the visual input, whereas humans are able to gather visual information with greater flexibility from large image regions.},
department = {Department Logothetis},
web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6VRT-4JS21WP-11-1\&_cdi=6243\&_user=29041\&_orig=browse\&_coverDate=04\%2F18\%2F2006\&_sk=999839991\&view=c\&wchp=dGLbVlb-zSkWz\&md5=08d41ae24c5163164abab077315779e5\&ie},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
DOI = {10.1016/j.cub.2006.03.027},
author = {Nielsen, KJ and Logothetis, NK and Rainer, G}
}
@Article { 3833,
title = {Fixations in natural scenes: interaction of image structure and image content},
journal = {Vision Research},
year = {2006},
month = {3},
volume = {46},
number = {16},
pages = {2535-2545},
abstract = {Explorative eye movements specifically target some parts of a scene while ignoring others. Here we investigate how local image structure - defined by spatial frequency contrast - and informative image content - defined by higher order image statistics - are weighted for the selection of fixation points. We measured eye movements of macaque monkeys freely viewing a set of natural and manipulated images outside a particular task. To probe the effect of scene content, we locally introduced patches of pink noise into natural images, and to probe the interaction with image structure, we altered the contrast of the noise. We found that fixations specifically targeted the natural image parts and spared the uninformative noise patches. However, both increasing and decreasing the contrast of the noise attracted more fixations, and, in the extreme cases, compensated the effect of missing content. Introducing delusive patches from another natural image led to similar results. In all paradigms tested, the interaction bet
ween scene structure and informative scene content was the same in any of the first six fixations on an image, demonstrating that the weighting of these factors is constant during viewing of an image. These results question theories, which suggest that initial fixations are driven by stimulus saliency whereas later fixations are determined by informative scene content.},
department = {Department Logothetis},
web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6T0W-4JHMFCW-1-B\&_cdi=4873\&_user=29041\&_orig=browse\&_coverDate=08\%2F31\%2F2006\&_sk=999539983\&view=c\&wchp=dGLbVtb-zSkWW\&md5=6cfbfebe283a94a24048473552a43f33\&ie=},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
DOI = {10.1016/j.visres.2006.02.003},
author = {Kayser, C and Nielsen, KJ and Logothetis, NK}
}
@Article { 3819,
title = {Eye movements of monkey observers viewing vocalizing conspecifics},
journal = {Cognition},
year = {2006},
month = {1},
volume = {101},
number = {3},
pages = {515-529},
abstract = {Primates, including humans, communicate using facial expressions, vocalizations and often a combination of the two modalities. For humans, such bimodal integration is best exemplified by speech-reading  humans readily use facial cues to enhance speech comprehension, particularly in noisy environments. Studies of the eye movement patterns of human speech-readers have revealed, unexpectedly, that they predominantly fixate on the eye region of the face as opposed to the mouth. Here, we tested the evolutionary basis for such a behavioral strategy by examining the eye movements of rhesus monkeys observers as they viewed vocalizing conspecifics. Under a variety of listening conditions, we found that rhesus monkeys predominantly focused on the eye region versus the mouth and that fixations on the mouth were tightly correlated with the onset of mouth movements. These eye movement patterns of rhesus monkeys are strikingly similar to those reported for humans observing the visual components of speech. The data therefore suggest that the sensorimotor strategies underlying bimodal speech perception may have a homologous counterpart in a closely related primate ancestor.},
department = {Department Logothetis},
web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6T24-4J5C802-1-K\&_cdi=4908\&_user=29041\&_orig=search\&_coverDate=10\%2F31\%2F2006\&_sk=998989996\&view=c\&wchp=dGLbVzz-zSkzS\&md5=44ee60f125ff59f612771fae32e6f567\&ie=/sdarticle.pdf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
DOI = {10.1016/j.cognition.2005.12.007},
author = {Ghazanfar, AA and Nielsen, KJ and Logothethis, NK}
}
@Inbook { 4317,
title = {Using spikes and local field potentials to reveal computational networks in monkey cortex},
year = {2008},
pages = {350-362},
abstract = {Traditionally, neurophysiological investigations in awake non-human primates have largely focused on the study of single-unit activity (SUA), recorded extracellularly in behaving animals using microelectrodes. The general aim of these studies has been to uncover the neural basis of cognition and action by elucidating the relation between brain activity and behavior. This is true for studies in sensory systems such as the visual system, where investigators are interested in how SUA covaries with aspects of visually presented stimuli, as well as for studies in the motor system where SUA covariation with movement targets and dynamics are investigated. In addition to these SUA studies, there has been increasing interest in the local field potential (LFP), a signal that reflects aggregate activity across populations of neurons near the tip of the microelectrode. In this chapter, we will describe recent progress in our understanding of brain function in awake behaving monkeys using LFP recordings. We will show that the combination of recording the activity of single neurons and local populations simultaneously offers a particularly promising way to gain insight into cortical brain mechanisms underlying cognition and memory.},
department = {Department Logothetis},
web_url = {http://ebooks.cambridge.org/chapter.jsf?bid=CBO9780511541650\&cid=CBO9780511541650A024},
editor = {H{\"o}lscher, C. , M. Munk},
publisher = {Cambridge University Press},
address = {Cambridge, UK},
booktitle = {Information processing by neuronal populations},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
ISBN = {978-0-521-87303-1},
DOI = {10.1017/CBO9780511541650.014},
author = {Nielsen, KJ and Rainer, G}
}
@Techreport { 2075,
title = {Psychophysical comparison of synthesis algorithms for natural images},
year = {2003},
month = {12},
number = {119},
abstract = {In this study, we used three computational algorithms to compute basis sets for natural
image patches, such that each patch could be synthesized as a linear combination of basis functions.
The two biologically plausible algorithms non-negative matrix factorization (NMF) and sparsenet
(SPN) were compared to standard principal component analysis (PCA). We assessed human
psychophysical performance at identifying natural image patches synthesized using different basis set
sizes in each of the algorithms. We also computed the reconstruction error, which represents a simple
objective measure of synthesis performance. We found that the reconstruction error was a good
predictor of human psychophysical performance. Performance was best for PCA, followed by NMF
and SPN despite large differences in basis function characteristics. All algorithms were well able to
generalize to represent novel natural image patches. When applied to white noise patches instead of
natural images, PCA and SPN outperformed NMF. This shows that of the three algorithms the one
that is least biologically plausible (PCA) actually supported best psychophysical performance,
suggesting that in the present study it is low-level quality of reconstruction that is the main
determinant of psychophysical performance.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf2075.pdf},
department = {Department Logothetis},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
institution = {Max Planck Institute for Biological Cybernetics},
author = {Nielsen, K and Logothetis, NK and Rainer, G}
}
@Poster { 5545,
title = {Neural encoding of species dependent face-categories in the macaque temporal cortex},
journal = {Neuroforum},
year = {2007},
month = {4},
volume = {13},
number = {Supplement},
pages = {767},
abstract = {When perceiving a face, we can easily decide whether it belongs to a human or non-human primate. It is
thought that face information is represented by neurons in the macaque temporal cortex. However, the precise
encoding mechanisms used by these neurons remain unclear. Here we use face stimuli of humans, monkeys
and monkey-human hybrids (morphs) to gain a better understanding of these mechanisms, in particular of the
categorization of faces into different species, and how learning affects representation of these stimuli.
We perform single cell and local field potential (LFP) recordings in the inferior-temporal (IT) cortex of the
macaque brain during a fixation task. To investigate the perceptual effects of our stimuli and possible relations
to the neural data, we conduct in parallel psychophysical experiments with human subjects. On preliminary
results of 75 recorded cells in one animal, we found 66 visual responsive neurons. From them, 12 were tuned
to faces ('face-cells') and 9 to other test objects (like a hand, clock, fruits, etc.). Six 'face-cells' prefer monkeys
while just two prefer humans. Considering the population activity, monkey faces elicited in general higher
firing rates on the population of neurons (independent of its category) than human faces. Additionally, these
firing rates change gradually according to the human/monkey ratio of the morphed stimuli. After measuring
the perceptual category boundary between monkeys and humans faces in our human subjects, we founded that
it is shifted to the human side, independent of the method we use to measure it.
Our preliminary cell recordings suggest that neural responses (firing rates) of some cells differentiate between
monkey and human faces. Besides, the tuning curves of some neurons and the population correlate with the
human-ratio of the morphed stimuli. Our psychophysical experiments confirm, on the one hand, the perceptual
effect of our stimuli in which we manipulate the human-monkey ratio and, on the other hand showed a
tendency of our subjects to set the category boundary between humans and monkeys closer to the human side.
All these findings point to different mechanisms used by the brain to encode human and monkey faces, which
seem to be clearly represented by neurons in the inferior-temporal cortex of the money brain.},
department = {Department Logothetis},
web_url = {http://www.neuro.uni-goettingen.de/nbc.php?sel=archiv},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {G{\"o}ttingen, Germany},
event_name = {7th Meeting of the German Neuroscience Society, 31st G{\"o}ttingen Neurobiology Conference},
author = {Sigala A., GR and Nielsen, K and Logothetis, NK and Rainer, G}
}
@Poster { 5551,
title = {Using 3-D human-monkey morphs to explore the boundaries of species dependent face-categories in humans},
journal = {Perception},
year = {2006},
month = {8},
volume = {35},
number = {ECVP Abstract Supplement},
pages = {207-208},
abstract = {Face perception has often been investigated with human faces differing in categories such as race or gender. Here, we investigate the perceptual border across species. We applied a method based on support vector machines to generate images of hybrid monkey - human faces (‘morphs‘) with different levels of human contribution. In the ‘explicit‘ experiment, we asked subjects to rate morphs at different morph levels as ‘humans‘ or ‘monkeys‘. We found that subjects rated the morphs as humans when they had a human contribution of at least 56\%±3\%. In the ‘implicit‘ experiment, we asked whether subjects could distinguish between successively presented morphs differing by ±10\% morph level from a morph centre. By varying the morph centre value from 10\% to 90\%, we were able to measure subject\&lsqu
o;s sensitivity to detect species differences along the human - monkey continuum. We found that the sensitivity of subjects to detect species differences was highest when morphs had a human contribution of 65\%±3\%. In summary, the human - monkey boundary does not lie at the midpoint of the human - monkey continuum, but tends to be shifted towards the human side. Our results reveal an asymmetry in the perception of human - monkey morphed faces, which may be species-specific and/or due to expertise.},
department = {Department Logothetis},
web_url = {http://pec.sagepub.com/content/35/1_suppl.toc},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {St. Petersburg, Russia},
event_name = {29th European Conference on Visual Perception},
language = {en},
DOI = {10.1177/03010066060350S101},
author = {Sigala, R and Koch, A and Nielsen, KJ and Logothetis, NK and Rainer, G}
}
@Poster { 5853,
title = {Inferior temporal cortex during real world vision},
year = {2006},
month = {6},
pages = {74},
abstract = {Much of current visual neuroscience is performed using standardized procedures. Most notably,
these generally include stimulus delivery using computer displays, the requirement of fixation,
repeated performance of experimental conditions and lengthy conditioning of animals on tasks to
allow for behavioral reports. Correlating neural responses with stimulus characteristics and
behavior lies at the heart of systems neuroscience. These controlled conditions have many
advantages, but at the same time can only represent an approximation of the processes that
occur during real world vision.
But how much are we missing under these constraints? Real world vision is characterized by eye
movements in three dimensions as observers fixate and track objects in the environment. What
are the characteristics of spike trains collected under such conditions and how do they differ from
those collected during task performance. How much can be said about neural activity by applying
the correlational approach to data acquired under these conditions? Does what we learn about
neural activity and selectivity during task performance generalize to real world vision? To begin to
address these questions, we have recorded extracellular activity of several inferior temporal
cortex neurons simultaneously while monkeys viewed face and object stimuli presented on a
computer monitor at the center of gaze during fixation. Then we record activity of the same
neurons during interaction with a human experimenter, while measuring the monkeys’ eye
position and recording the visual input using a camera. We compare about 5 minutes of activity
collected during these two conditions. Preliminary results suggest many IT neurons were
dynamically modulated during real world vision. Peak firing rates (eg at 200ms binwidth) tended
to be greater during real world vision than during task performance. Some IT neurons showed
markedly different interspike interval distributions in the two conditions.
Our findings suggest that a dynamic three dimensional visual environment may be a useful tool
for elucidating the function of visual neurons.},
department = {Department Logothetis},
web_url = {http://www.areadne.org/2006/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Santorini, Greece},
event_name = {AREADNE 2006: Research in Encoding and Decoding of Neural Ensembles},
language = {en},
author = {Sigala, R and Liebe, S and Nielsen, K and Logothetis, NK and Reiner, G}
}
@Poster { 3642,
title = {The influence of behavioral relevance on object representation in inferior temporal cortex},
year = {2004},
month = {10},
volume = {34},
number = {751.4},
abstract = {Partial occlusion of objects is common in natural environments, and in most cases does not affect the identification of the occluded object. However, under certain conditions identification fails. The distinction between the two cases lies in which object parts remain visible through the occluder. We have recently shown for Rhesus monkeys performing a discrimination task on sets of natural images that the occlusion of specific image regions systematically influences behavioral performance. Here, we report on how these differences between image regions influence the responses of area IT neurons to partially occluded images.
For four natural images, we determined three partially occluded variants that were reliably identified by the monkeys, and three variants that the monkeys failed to identify correctly. Images and their occluded variants were specific for each monkey observer. The three variants of each category differed in the image portion visible through the occluder (10, 30 or 50\%). We recorded from 341 IT neurons in two monkeys. 102 neurons were selected because their preferred non-occluded image evoked responses significantly different from baseline (p